Method for producing high melting point crystals of phenoxypropionic acid derivative

ABSTRACT

A method for producing high melting point crystals, which is characterized by heating ethyl=(R)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate in the form of low melting point crystals, or low melting point crystals and high melting point crystals, within a range of from 50° C. to lower than the melting point of the low melting point crystals.

TECHNICAL FIELD

[0001] The present invention relates to a method for producing highmelting point crystals (hereinafter referred to as β-crystals) ofethyl=(R)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate (hereinafterreferred to as quizalofop-p-ethyl) and β-crystals thereby produced.

BACKGROUND ART

[0002] Quizalofop-p-ethyl which is useful as an active ingredient for aherbicide, is known to have two types of crystal forms, i.e. low meltingpoint crystals (hereinafter referred to as α-crystals) and β-crystals.JP-B-4-76721 discloses that β-crystals can be produced by graduallycooling a solution having quizalofop-p-ethyl dissolved in a solvent,with stirring and maintaining it at a crystallizing temperature, and theproduced β-crystals are ones having crystallites of at most 1 μmagglomerated, whereby in some cases, transfer of the solvent slurry, orfiltration and drying of the precipitated crystals, are difficult.

DISCLOSURE OF INVENTION

[0003] It is an object of the present invention to provide β-crystalswhich are easy to handle in an industrial scale and a method for theirproduction.

[0004] The present invention provides a method for producing β-crystals,which is characterized by heating quizalofop-p-ethyl in the form ofα-crystals, or α-crystals and β-crystals, within a range of from 50° C.to lower than the melting point of α-crystals, and β-crystals producedby such a method.

[0005] The heating can be carried out by heating in contact with a hightemperature innert gas (hereinafter referred to as a gas-solid heatingmethod), heating with mixing in a solid state (hereinafter referred toas a solid heating method) or heating in suspension with a hardlysoluble solvent (hereinafter referred to as a suspension heatingmethod).

[0006] The gas-solid heating method may, for example, be a methodwherein quizalofop-p-ethyl is charged into an apparatus equipped with agas-solid contact function such as a pneumatic conveying dryer, afluidized bed dryer, a circulation dryer or a hot air dryer, and a hightemperature gas such as heated air or heated nitrogen is blown thereintofor heat treatment.

[0007] The solid heating method may, for example, be a method whereinquizalofop-p-ethyl is charged into an apparatus equipped with a heatingmeans such as a jacketed kneader, an agitation drier, a jacketed screwconveyer or a conical drier and provided with a mixing function, andheated and mixed for a predetermined period of time.

[0008] The suspension heating method may, for example, be a methodwherein quizalofop-p-ethyl is charged to a hardly soluble solvent suchas water or ethylene glycol, and heated in suspension.

[0009] The heating can be carried out usually at a temperature of from50° C. to lower than the melting point of α-crystals, preferably from65° C. to lower than the melting point of α-crystals.

[0010] The heating time usually depends on the heating temperature andis required to be a time until α-crystals have substantiallydisappeared. For example, it takes at least 100 hours when heating iscarried out at 60° C. and a few hours when heating is carried out at 70°C., to obtain β-crystals.

[0011] After α-crystals have been converted to β-crystals by heating,cooling, or cooling followed by filtration in the suspension heatingmethod, is carried out to obtain β-crystals.

[0012] In the gas-solid heating method and the solid heating method,β-crystals can be obtained in a solid state, and can be used as it is,or after pulverization, for example, for the production of an aqueoussuspension concentrate.

[0013] Further, in the gas-solid heating method or the solid heatingmethod, if quizalofop-p-ethyl mainly in the form of α-crystals producedby crystallization method, is employed, the resulting β-crystals will beobtained in a powder form without forming a block solid in the aboveapparatus, whereby high productivity can be maintained. In such a case,it is preferred to employ quizalofop-p-ethyl mainly in the form ofα-crystals containing substantially no solvent for crystallization.JP-B-2-214504 discloses that α-crystals obtained as a wet product by acrystallization method may sometimes change into β-crystals when driedat a temperature exceeding 70° C. for at least 5 hours. However, if sucha wet product containing a solvent for crystallization is used,dissolution by the solvent takes place during the heating, and theproduct is likely to be an aggregated solid in the apparatus, wherebyindustrial operation is practically difficult.

[0014] In the suspension heating method, removal of the hardly solublesolvent may sometimes be required. For example, when the hardly solublesolvent is water, a drying step may sometimes be required. However, in acase where an aqueous suspension agricultural chemical composition is tobe obtained, drying will not be required depending upon the weightconcentration of the suspension. Further, by the suspension heatingmethod, the dispersed state in the apparatus can be excellentlymaintained during the heating operation, whereby the temperature controlof quizalofop-p-ethyl is easy, and uniform β-crystals can be producedefficiently. Further, β-crystals formed by the suspension heating methodare excellent in the filtration property and easy for drying.

[0015] Now, a method for obtaining desired β-crystals by suspending thestarting material in water which is the hardly soluble solvent and whichis industrially inexpensive, will be described.

[0016] Namely, quizalofop-p-ethyl in the form of α-crystals, orα-crystals and β-crystals, is suspended in water usually in an amount offrom 0.1 to 60 wt %, preferably from 1 to 60 wt %, and the suspension ismaintained at a temperature of from 50° C. to lower than the meltingpoint of α-crystals until α-crystals substantially disappears,preferably at a temperature of from 65° C. to lower than the meltingpoint of α-crystals for from 10 minutes to 48 hours. Thereafter, it iscooled to a temperature where usually filtration can be carried out,usually at most 50° C., preferably at most 40° C., followed byfiltration to collect crystals. When the crystals have been completelyconverted to β-crystals, drying of the crystals can be carried out at atemperature lower than the melting point of β-crystals, usually lowerthan the melting point of α-crystals, preferably at most 65° C.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] Now, the present invention will be described in further detailwith reference to Examples. However, it should be understood that thepresent invention is by no means restricted to such specific Examples.The weight ratio of α-crystals and β-crystals approximates the arearatio of the respective endothermic peaks obtained by the differentialscanning calorimetry and thus was obtained from the area ratio of therespective endothermic peaks.

EXAMPLE 1

[0018] Into a 20 l double-screw U-trough type jacketed kneader, 20 kg ofα-crystals of quizalofop-p-ethyl containing 0.2 wt % of β-crystals, werecharged and mixed. Warm water was circulated to the jacket to raise thetemperature to 70° C. Four hours later, the differential scanningcalorimetry of quizalofop-p-ethyl was carried out, whereby it wasconfirmed that the entire amount had been converted to β-crystals.

EXAMPLE 2

[0019] In the same manner as in Example 1, heating was carried out at65° C. for 16 hours, and then the differential scanning calorimetry ofquizalofop-p-ethyl was carried out, whereby it was confirmed that theentire amount had been converted to β-crystals.

EXAMPLE 3

[0020] Into a 10 l agitation drier, 5 kg of α-crystals ofquizalofop-p-ethyl containing 0.2 wt % of β-crystals, were charged andmixed. Warm water was circulated to the jacket to raise the temperatureto 72.5° C. Two hours later, the differential scanning calorimetry ofquizalofop-p-ethyl was carried out, whereby it was confirmed that theentire amount had been converted to β-crystals.

EXAMPLE 4

[0021] Into a 5 l conical drier, 1 kg of α-crystals ofquizalofop-p-ethyl containing 0.2 wt % of β-crystals, were charged andmixed. Warm water was circulated to the jacket to raise the temperatureto 55° C. Two months later, the differential scanning calorimetry ofquizalofop-p-ethyl was carried out, whereby it was confirmed that theentire amount had been converted to β-crystals.

EXAMPLE 5

[0022] Into a 10 l conical flash drier, 3 kg of α-crystals ofquizalofop-p-ethyl containing 0.2 wt % of β-crystals, were charged, andhot air was blown into it to raise the temperature to 70° C. Four hourslater, the differential scanning calorimetry of quizalofop-p-ethyl wascarried out, whereby it was confirmed that the entire amount had beenconverted to β-crystals.

EXAMPLE 6

[0023] In the same manner as in Example 5, heating was carried out at65° C. for 16 hours. Then, the differential scanning calorimetry ofquizalofop-p-ethyl was carried out, whereby it was confirmed that theentire amount had been converted to β-crystals.

EXAMPLE 7

[0024] Into a 5 l fluidized drier, 1 kg of α-crystals ofquizalofop-p-ethyl containing 0.2 wt % of β-crystals, was charged andhot air was blown into it to raise the temperature to 70° C. Four hourslater, the differential scanning calorimetry of quizalofop-p-ethyl wascarried out, whereby it was confirmed that the entire amount had beenconverted to β-crystals.

EXAMPLE 8

[0025] Into a 2 l jacketed reaction flask, 60 g of α-crystals ofquizalofop-p-ethyl containing 0.2 wt % of crystals, and 240 g of water,were charged to prepare a 20 wt % suspension solution. Warm water wascirculated to the jacket, and the suspension solution was heated to72.5° C. with stirring. Two hours later, a part of quizalofop-p-ethylsuspended in the solution, was collected by filtration and dried,whereupon the differential scanning calorimetry was carried out, wherebyit was confirmed that the entire amount had been converted toβ-crystals.

[0026] Then, the warm water in the jacket was withdrawn, and the abovesuspension solution was cooled. After cooling, quizalofop-p-ethylsuspended in the solution was collected by filtration at roomtemperature and dried at about 55° C. Then, the differential scanningcalorimetry was carried out, whereby it was confirmed that the entireamount was maintained to be β-crystals.

EXAMPLE 9

[0027] Into a 2 l jacketed reaction flask, 120 g of α-crystals ofquizalofop-p-ethyl containing 0.2 wt % of β-crystals, and 180 g ofwater, were charged to prepare a 40 wt % suspension solution. Warm waterwas circulated to the jacket, and the suspension solution was heated to70° C. with stirring. Twenty hours later, a part of quizalofop-p-ethylsuspended in the solution was collected by filtration and dried at 45°C. Then, the differential scanning calorimetry was carried out, wherebyit was confirmed that the entire amount had been converted toβ-crystals.

EXAMPLE 10

[0028] Into a 2 l jacketed reaction flask, 40 g of α-crystals ofquizalofop-p-ethyl containing 10 wt % of β-crystals, and 240 g of water,were charged to prepare an about 14 wt % suspension solution. Warm waterwas circulated to the jacket, and the suspension solution was heated to70° C. with stirring. Four hours later, a part of quizalofop-p-ethylsuspended in the solution was collected by filtration and dried. Then,the differential scanning calorimetry was carried out, whereby it wasconfirmed that the entire amount had been converted to β-crystals.

[0029] Then, the warm water in the jacket was withdrawn, and the abovesuspension solution was cooled. After cooling, quizalofop-p-ethylsuspended in the solution was collected by filtration and dried at about50° C. Then, the differential scanning calorimetry was carried out,whereby it was confirmed that the entire amount was maintained to beβ-crystals.

EXAMPLE 11

[0030] Into a 2 l jacketed reaction flask, 15 g of α-crystals ofquizalofop-p-ethyl containing 10 wt % of β-crystals, and 240 g of water,were charged to obtain an about 6 wt % suspension solution. Warm waterwas circulated to the jacket, and the suspension solution was heated to70° C. with stirring. Six hours later, a part of quizalofop-p-ethylsuspended in the solution was collected by filtration and dried. Then,the differential scanning calorimetry was carried out, whereby it wasconfirmed that the entire amount had been converted to β-crystals.

[0031] Then, the warm water in the jacket was withdrawn, and the abovesuspension solution was cooled. After cooling, quizalofop-p-ethylsuspended in the solution was collected by filtration and dried at about55° C. Then, the differential scanning calorimetry was carried out,whereby it was confirmed that the entire amount was maintained to beβ-crystals.

EXAMPLE 12

[0032] In the same manner as in Example 11, heating was carried out at65° C. for 16 hours. Then, a part of quizalofop-p-ethyl suspended in thesolution was collected by filtration and dried. Then, the differentialscanning calorimetry was carried out, whereby it was confirmed that theentire amount had been converted to β-crystals.

[0033] Then, the warm water in the jacket was withdrawn, and the abovesuspension solution was cooled. After cooling, quizalofop-p-ethylsuspended in the solution was collected by filtration at roomtemperature and dried at about 60° C. Then, the differential scanningcalorimetry was carried out, whereby it was confirmed that the entireamount was maintained to be β-crystals.

EXAMPLE 13

[0034] In the same manner as in Example 11, heating was carried out at60° C. for three days. Then, a part of quizalofop-p-ethyl suspended inthe solution was collected by filtration and dried. Then, thedifferential scanning calorimetry was carried out, whereby it wasconfirmed that the entire amount had been converted to β-crystals.

[0035] Then, the warm water in the jacket was withdrawn, and the abovesuspension solution was cooled. After cooling, quizalofop-p-ethylsuspended in the solution was collected by filtration at roomtemperature and dried at about 45° C. Then, the differential scanningcalorimetry was carried out, whereby it was confirmed that the entireamount was maintained to be β-crystals.

EXAMPLE 14

[0036] In the same manner as in Example 11, heating was carried out at67.5° C. for 10 hours. Then, a part of quizalofop-p-ethyl suspended inthe solution was collected by filtration and dried. Then, thedifferential scanning calorimetry was carried out, whereby it wasconfirmed that the entire amount had been converted to β-crystals.

[0037] Then, the warm water in the jacket was withdrawn, and the abovesuspension solution was cooled. After cooling, quizalofop-p-ethylsuspended in the solution was collected by filtration at roomtemperature and dried at about 60° C. Then, the differential scanningcalorimetry was carried out, whereby it was confirmed that the entireamount was maintained to be β-crystals.

EXAMPLE 15

[0038] Into a 1,000 l jacketed agitation tank, 25 kg of α-crystals ofquizalofop-p-ethyl containing 0.2 wt % of β-crystals, and 475 kg ofwater, were charged to prepare a 5 wt % suspension solution. Warm waterwas circulated to the jacket, and the suspension solution was heated to70° C. with stirring. Eight hours later, a part of quizalofop-p-ethylsuspended in the solution was collected by filtration and dried. Then,the differential scanning calorimetry was carried out, whereby it wasconfirmed that the entire amount had been converted to β-crystals.

[0039] Then, the above suspension solution was subjected to filtrationby a 65 l centrifugal separator. The product was dried at 60° C. by a600 l conical drier in vacuum to obtain a dried product of β-crystals ofquizalofop-p-ethyl.

1. A method for producing high melting point crystals, which ischaracterized by heatingethyl=(R)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate in the formof low melting point crystals, or low melting point crystals and highmelting point crystals, within a range of from 50° C. to lower than themelting point of the low melting point crystals.
 2. The method accordingto claim 1, wherein the heating is heating in contact with a hightemperature inert gas, heating with mixing in a solid state, or heatingin suspension with a hardly soluble solvent.
 3. The method according toclaim 1, wherein the heating is heating in suspension with a hardlysoluble solvent.
 4. The method according to claim 3, wherein the hardlysoluble solvent is water.
 5. The method according to claim 4, whereinfrom 1 to 60 wt %, based on the water, ofethyl=(R)-2-[4-(6-chloro-2-quinoxalyloxy)phenoxy]propionate issuspended.
 6. High melting point crystals produced by the method asdefined in claim 1.